OnError event have a bad behavior with the showPreview option

[BakasuraRCE]

Prerequisites

• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• The issue still exists against the latest master branch of bootstrap-fileinput.
• This is not an usage question. I confirm having read the plugin documentation and demos.
• This is not a general programming / coding question. (Those should be directed to the webtips Q & A forum).
• I have attempted to find the simplest possible steps to reproduce the issue.
• I have included a failing test as a pull request (Optional).

Steps to reproduce the issue

1. Set showPreview to false
2. Create an error event handler
3. Upload any file
4. Return an invalid response in the server
5. The error happend

Expected behavior and actual behavior

The variable $thumb is not defined when showPreview are disabled:

bootstrap-fileinput/js/fileinput.js

Line 2146 in 5911e2c

self._setPreviewError($thumb, i, self.filestack[i], self.retryErrorUploads);

Other events have a checker about it:

bootstrap-fileinput/js/fileinput.js

Line 2095 in 5911e2c

if (self.showPreview) {

fileinput.js:3017 Uncaught TypeError: Cannot read property 'find' of undefined
    at FileInput._refreshUploadButton (fileinput.js:3017)
    at FileInput._setPreviewError (fileinput.js:3014)
    at fileinput.js:2146